Who plans what?

Re the previous post, Paul Romer and David Miller discuss city layout and growth in this conversation.  They mention the long-term advantages of a laying out plans for a street grid.  For the cases of New York and Toronto, there were advantages such as better bus routing options. But how many central cities of big metros are now being planned -- with the plausible exception of Third World cities?

I alluded to a division of labor whereby land use planning as well as complementary infrastructure planning are private.  Somewhere up the line, the private infrastructure can hook up with a larger, perhaps public, system.

Randy Holcombe has suggested another division of labor whereby public planners take care of infrastructure and private planners take care of the land use plans.

Planning is very hard work and can be overwhelming.  Let's not overburden anyone.  Let's discover divisions of labor that work best.  Let's not simply suppose that it can all be done by the same public agencies.